The present invention relates to a deceleration-sensitive braking pressure control device for a vehicular hydraulic brake system wherein the small active surface of a spring-loaded stepped piston is a boundary for an inlet chamber connected with a braking pressure generator while the larger active surface of this piston is a boundary for an outlet chamber connected with at least one wheel brake cylinder. Via a channel, the inlet and outlet chambers communicate with a valve which is formed by a closure member, in particular a ball, disposed in the inlet chamber, which closure member is movable in a deceleration-sensitive manner, and by a valve seat at the adjacent end of the stepped piston. A stop is provided for the closure member, which, in the rest position of the stepped piston, guarantees a minimum distance between the closure member and the valve seat, and the end of the stepped piston adjacent the inlet chamber is surrounded by a sleeve.
In a known device of this type, for instance, German Patent DE-AS No. 2,213,496, the stop for the closure member and the sleeve are arranged so as to be fastened with the housing. With the inlet pressure gradually increasing, the stepped piston will move against the force of its spring towards the inlet chamber due to its different active surfaces. At a predetermined change-over pressure the minimum distance will have been travelled. Now, the valve may close dependent on the deceleration-sensitive movement of the closure member. The valve being closed, the associated second branch of the characteristic curve of the device has a smaller inclination than the first branch while the valve was open. On the side of the closure member opposite the stop there is an abutment fastened to the housing. The distance between the abutment and the stop approximately amounts to twice the axial length of the closure member.
In this construction, the change-over pressure and the inclinations of the branches of the characteristic curve of the pressure depend on each other. This impairs the optimum rating of the braking pressure control device. If, due to a malfunction, the closure member remains at the abutment, the valve will not be effective at all, the device failing altogether and the danger of a lock-up increasing considerably upon an operation of the rear wheel brakes.